Ores and various concentrates of ores which contain valuable metals such as nickel, copper, zinc, lead, etc. as simple or complex sulfides together with small amounts of the precious metals gold and silver and platinum group metals present in various forms including distinct sulfidic, selenic and telluric species are almost universally concentrated by froth flotation using xanthates or other sulfur-containing collectors. The various schemes of froth flotation employed are generally quite complex having been developed in order to maximize grade and recovery of the valuable metals present and to maximize discarding of rock and mineral species of little commercial value. In addition to strictly sulfide minerals, certain oxide or carbonate species of metals such as copper can also be floated. In floating these oxide or carbonate minerals such as cuprite, malachite, azurite, chrysocolla, etc., ground mineral surfaces can be sulfided by reagents such as sodium sulfide carried in the liquid continuum of the flotation pulp or can be rendered amenable to flotation by overdosing with a collector such as a xanthate. For purposes of this specification and claims the term "flotable non-ferrous metal-containing mineral" is intended to include, but not be limited to, the mineral species chalcopyrite, chalcocite, pentlandite, niccolite, millerite, stannite, cuprite, malachite, galena, stibnite, heazlewoodite, argentite, covellite, sperrylite, cinnabar, cubanite, cobaltite, skutterudite and smaltite.
After concentration, sulfidic minerals are most often subjected to pyrometallurgical oxidation, a bi-product of which is sulfur dioxide. Good practice, as well as governmental orders, requires that sulfur dioxide released to the atmosphere be minimized. Sources of sulfur often present in ore bodies are the minerals pyrrhotite, pyrite and marcasite. Pyrrhotite has a composition roughly Fe.sub.8 S.sub.9 and is symbolized hereinafter as Px. In many ores Px carries with it very little material of economic value but does contain sulfur which contributes to the sulfur dioxide burden. Px can be either strongly ferromagnetic, in which case it can be separated by magnetic separation, or paramagnetic in which case magnetic separation is not practical. In the past, procedures such as the Inco-developed cyanide process, Canadian Patent No. 1,062,819 and the SO.sub.2 /air process (patent pending) have been developed to maximize rejection of Px during flotation. These processes in general have been successful but often require extensive conditioning of mineral pulps to be reasonably operable.